Computational insights into the corrosion inhibition mechanism of daidzein on Al(AA7075) alloy in NaCl solution: A DFT and molecular dynamics study.

This study employs a combined Density Functional Theory (DFT) and Molecular Dynamics (MD) approach to elucidate the corrosion inhibition mechanism of daidzein on the Al(AA7075) surface in a NaCl environment. DFT results reveal that the neutral daidzein molecule (DZIN) possesses favorable electronic characteristics for adsorption, including a relatively small HOMO-LUMO energy gap of 4.398 eV, an ionization potential of 6.101 eV, and a high electrophilicity index of 3.462 eV, indicating strong electron-donation and acceptance capabilities. The fractional electron transfer (ΔN = 0.231) confirms efficient charge exchange with aluminum, supported by a low chemical hardness (η = 2.199 eV) and high softness (σ = 0.455), which collectively enhance its surface reactivity. Molecular Electrostatic Potential (MEP) and Mulliken charge analyses further identify carbonyl and hydroxyl oxygen atoms as dominant adsorption centers due to their highly negative potentials. Complementary MD simulations demonstrate that neutral daidzein exhibits a remarkably strong interaction energy of -130.23 kcal mol-1, significantly outperforming its protonated form (-35.55 kcal mol-1), enabling it to form a compact, adherent protective film through π-metal interactions and van der Waals stabilization. The combined DFT-MD findings confirm that the superior inhibition performance of daidzein arises from its strong electron-donating functional groups, favorable charge-transfer characteristics, and highly stable adsorption configuration on aluminum, making it a highly efficient, bio-derived corrosion inhibitor for mitigating chloride-induced degradation of Al(AA7075) surfaces.